A Coating Change That Invalidates a Food Contact Declaration
A raw material shift in barrier coatings alters chemical migration profiles, instantly invalidating food contact declarations and risking complete job quarantine.
Cobb 60 Absorbency
Water Absorption
A standardised test measures the mass of water absorbed by one square metre of paperboard in sixty seconds. This measurement determines the wetting resistance of paper and paperboard substrates intended for aqueous environments. In the board manufacturing process, cobb 60 absorbency is a critical parameter that indicates how the material will behave during storage in humid warehouses or when exposed to accidental moisture.
Sizing Control
Sizing agents added to the pulp or applied at the size press govern cobb 60 absorbency by altering the surface energy of fibres. Alkyl ketene dimer or alkenyl succinic anhydride are commonly distributed throughout the stock to prevent capillary action from drawing liquid into the paperboard matrix. When sizing is insufficient, the paperboard quickly absorbs water, resulting in reduced structural strength and potential failure of the package.
Performance Validation
Converting operations like gluing and water-based printing require precise control over the rate of water absorption. If the values are too high, water-based inks will feather and bleed, ruining the graphic definition on the carton. Conversely, when the value is too low, aqueous adhesives cannot penetrate the surface fibres to create a fiber-tearing bond, which causes the package seams to fail during high-speed filling lines where rapid setting is essential.
This balance is maintained by adjusting the chemical dosage at the paper machine, allowing the converter to run at maximum speeds without risking adhesive delamination or printing defects.